Ever since my first introduction to physics, I have wondered about the meaning of energy. My high-school physics teacher once explained that energy comes in many forms, at which point I asked what unites all the forms. He described the law of conservation of energy, but I then asked what was being conserved. He was never able to give me a satisfactory answer, so I eventually stopped asking. Those sorts of questions became less urgent as I went on to study more advanced physics, but they continued to linger.
Nuclear physicist Jennifer Coopersmith's Energy, the Subtle Concept: The Discovery of Feynman's Blocks from Leibniz to Einstein is intended for people who, like me, wonder what energy really means. Coopersmith begins with an anecdote from Richard Feynman about a mother who observes that her son always has the same number of building blocks. Sometimes the blocks are hidden from view—for example,...
